1. Field of the Invention
The present invention relates generally to an ice making machine and more particularly to an automated ice making machine provided with a water level control device which is disposed within a sub-tank in fluid communication with an icing water tank to detect the water surface level within the icing water tank.
2. Description of the Prior Art
An example of an automated ice making machine of the type mentioned above has already been proposed, as in Japanese Patent Application Laid-Open No. 291,876/1986 (JP-A-No. 61-291,876) filed in the name of the inventor of the present application. FIG. 4 in the accompanying drawings shows a general arrangement of a water flow system incorporated in the prior art ice making maching mentioned above. In this figure, reference numeral 1 denotes an ice making plate equipped with an evaporator pipe 2 mounted thereon in a meandering pattern. An icing water tank 4 containing icing water (i.e. water to be transformed into ice) is disposed beneath the ice making plate 1 with a dropping water guide plate 3 being interposed therebetween. Provided in fluid communication with the icing water tank 4 is a water circulation pump 5 which serves to circulate the icing water during the freezing or icing mode so that the water is distributed over a surface of the ice making plated 1 from an icing water distributor 6 disposed above the ice making plate 1.
On the other hand, a water supply valve 7 connectable to a water supply source such as an external water service system is connected to a second defreezing or deicing water distributor 9 through a T-joint 8. Extending downwardly from the leg of the T-joint 8 is a flush pipe 10 which is connected to a connector pipe 12 of a sub-tank 11 provided in fluid communication with the icing water tank 4. In a deicing operation mode, the water supply valve 7 is opened, whereby water from the water service system is distributed over the rear surface of the ice making plate 1 from the second water distributor 9 and at the same time is supplied to the sub-tank 11 by way of the flushing pipe 10. The deicing water distributed over the rear surface of the ice making plate 1 drops into the icing water tank 4 through the guide plate 3 to be collected therein as the water to be iced in the succeeding ice making cycle. On the other hand, the water supplied to the sub-tank 11 washes it and thence flows into the icing water tank 4 through the connector pipe 13. A major part of water flowing into the icing water tank 4 is discharged outwardly through an overflow pipe 14.
The upper limit of the water level within the icing water tank 4 is defined by the overflow pipe 14. During the icing operation cycle, water within the icing water tank 4 is circulated by the circulation pump 5 to be supplied to the ice making plate assembly 1, with result in that crescent-shaped ice pieces 15 are formed on the front surface of the ice making plate 1 and grow progressively in the course of time. When the ice pieces have grown to a certain size, the amount of water within the tank 4 has been decreased by an amount corresponding to the water consumed in forming the ice pieces. Since the icing water tank 4 is in fluid communication with the sub-tank 11 through the connecting pipea 13, the water level within the latter is also lowered correspondingly. Consequently, the water surface within the connector tube 12 which had been at a considerably higher level at the start of the icing operation cycle, as shown in FIG. 5 of the accompanying drawings, is progressively lowered down to a level where the water surface lies below the bottom end 12a of the connector pipe 12. At that time, a chamber 16 defined within the sub-tank 11 and hermetically closed until then is opened to the atmosphere through a vent orifice (not shown) formed in the joint 8. As a result, a float 17 is caused to move downwardly. When the float 17 has attained a predetermined position, a magnet 18 mounted on the float 17 actuates a reed switch 19, whereby a signal indicating completion of the ice making operation is generated to thus bring the icing operation cycle to an end.
In the prior art ice making machine described above, such an arrangement is adopted so that impurities sedimented and deposited within the sub-tank 11 are driven into the icing water tank 4 through the connecting pipe 13 under the washing action by a part of the deicing water flowing into the sub-tank 11 through the flushing pipe 10 during the deicing operation cycle. In practice, however, there may arise such a situation in which the deicing water can not be supplied to the sub-tank 11 in amounts great enough to drive or carry the impurities into the icing water tank 4 because of flow resistance presented by the joint 8 as well as for other reasons. This problem may be solved by increasing the flow of water through the water supply valve 7 thereby increasing the water supply to the sub-tank 11. In that case, however, the amount of deicing water dropping into the icing water tank 4 from the ice making plate 1 is naturally increased, with the result that the amount of water discharged outwardly through the overflow pipe 14 is also increased, which in turn means that water consumption is wastefully increased, giving rise to other problems.